Robot arms, or computer controlled jointed and articulated manipulators, are known in the art for accomplishing numerous routine positioning and placement functions. Robot arms utilizing one or more pivotally joined arm members and terminating in a hand or end effector typically require a number of controlled motor drives to control the motion in one or more degrees of freedom between the arm members at each joint or elbow. In addition, each motor must be coordinated with all other motors through computer control in order to provide a prescribed motion for the end effector in accomplishing its various routine positioning or manipulation task.
In the semiconductor processing industry it is typical for a single semiconductor wafer to be processed through a plurality of tests for parameters such as thickness, resistivity, surface characteristics, etc. Typically the wafers are passed from a cassette, one wafer per slot, and one wafer at a time through the test stations into a recepticle cassette until an entire cassette full of wafers has been processed. The task of moving the wafers from cassette to cassette through the various test stations is typically automated using sophisticated elevator and conveyor belt mechanisms in order to accurately position the wafer at each test station and to place it in an output cassette in a location to which the data taken at the test station can be associated.